Experiment and simulation method are adopted to analyze the bolts fracture of the power take-off box of a certain type of dry-mixed mortar transport truck. The power take-off box gets power from the gear box and sends it to the air compressor through transport shaft, the materials are transported to the storehouse through the air pressure. The torque of transport shaft is measured at different rotation velocity. Results show that the torque value is high value and high aptitude at low rotation velocity. The analysis results of the fatigue life of bolts at the toque of different rotation velocity indicated the lower the current speed, the shorter the fatigue life of the power take-off bolt. It is concluded that air compressor working at low speed is the reason for the bolts fracture problem. The problem of the power take-off box bolt was solved by keeping the speed of air compressor at 950 r/min through the constant speed cruise function of the dry hybrid vehicle.